Winding machines of the type used to build up large packages of synthetic filament yarns typically employ overhung or cantilever mandrels about which the yarns are wound as the mandrels rotate about their axes. Such machines will be referred to here at times as spooling frames and the yarn packages as spools. The cantilever or overhung type mounting for such a mandrel leaves one end of the mandrel free and accessible for the endwise insertion thereover of empty fiber (e.g. paper) tubes onto which the yarn may be wound and for the endwise removal therefrom of the full yarn packages formed as a result of the winding of the yarn onto the fiber tubes.
To reduce vibrations associated with operation of such winding machines or spooling frames at high speeds, the spool mandrels may be mounted elastically. When the weight on such a mandrel is not great, it will be rotated about a generally horizontal axis. However, with spool mandrels which are elastically mounted on the machine at one end only, as is customary for overhung or cantilever mounted mandrels, the spool axis will assume a slanted position as the weight of the spool increases. That is, the free end of the mandrel will shift downwards. Downward shifting of the free end of the mandrel also can be expected in machines wherein the mandrel is not elastically mounted, because the weight of the yarn packages exerts bending forces on the mandrel.
In the absence of other factors, such shifting of the mandrel would affect the relationship between the outer surface of the yarn packages and the contact roll intended to bear thereagainst during the winding operation. In some machines the contact roll is the driving roll for rotating the mandrel through friction with the yarn package on the mandrel. In other machines the contact roll is a speedometer roll which frictionally contacts the outer surface of the building yarn package to sense the peripheral speed thereof and provide an input signal for a drive for the mandrel. In all of these cases, however, it is desirable that the contact roll press with reasonable uniformity against substantially the entire length of all the yarn packages being wound on a mandrel at a given time.
The contact roll ordinarily is disposed above the operative position of the mandrel on which the yarn packages are wound. Its mounting arrangement is such that it may move vertically as necessary in view of the changing diameter of the yarn packages as these are being built up. Means also are provided to press the contact roll downwardly to provide the desired contact with the peripheries of the yarn packages.
During a winding operation, as the weight of the yarn packages on a mandrel increases and the cantilever mounted mandrel consequently sags more and more, there is a tendency for the intended parallelism of the axes of the mandrel and contact roll to be affected adversely. This causes the pressing force of the contact roll against the yarn package to be increasingly reduced towards the free or overhung end of the mandrel.
U.S. Pat. No. 4,087,055 discloses a winder in which the mounting of a contact roll permits some tilting of the contact roll axis in response to sagging of a mandrel axis. In this apparatus a driving roll is mounted pivotably so that it can follow the sloping rotational axis of the spool mandrel as the yarn packages increase in weight.
In order that the driving roll may press with essentially the same force along the entire length of the spool, the roll is moved upwards, radially parallel to the axis of the spool mandrel, as the diameter of the spool increases. For this purpose, it is mounted at both of its ends in a pivotable yoke, which is carried on the machine frame for vertical movement relative to the axis of the mandrel. A spring or the like may bias the pivotable yoke to compensate for the imbalance tendencies associated with the weight of the driving roll and/or its drive motor.